The newspaper photo of D.A. Burr, who is played by Danny DeVito, is actually one of DeVito's character Louie DePalma from the T.V. show Taxi (1978), and was also used for character "Frank Stedman", also played by Danny Devito, in the movie "Head Office".
The closing credits jokingly bill two writers Neal Israel and Pat Proft who did not co-write the movie as "Special Medical Advisers". Neal Israel, also a director, was the second husband of the film's director Amy Heckerling and were married around the time that this movie was made and released.
While the movie sends up classic gangster movies in general, the basic plot point of Johnny and Tommy Kelly ending up on opposite sides of the law is inspired by "Manhattan Melodrama". In that film, William Powell and Clark Gable portray orphans who are raised together as brothers. Clark Gable's character "Blackie Gallagher" grows up to become a gangster while William Powell's character Jim Wade becomes a crusading DA (Just like Johnny and Tommy, respectively). Also in both films the gangster brother roots for the DA brother to succeed.
The rival crime boss in this film is named Maroni, a named shared by a major crime boss in the Batman universe. Michael Keaton would later appear onscreen as the Caped Crusader in Batman (1989) and Batman Returns (1992)
When Johnny discusses going 'legit' with Lil, they happily envision all the wonderful things offered by such a lifestyle. One of the benefits cited by Johnny was the ability to 'Say "hi" to a neighbor named Fred'. This was a clear tip of the hat to Fred Rogers, as Michael Keaton got started in the industry by working as a stagehand on 'Mister Rogers Neighborhood', when he was a young man still living in his native Pittsburgh. So close was their friendship that, when Fred Rogers died in 2003, Michael Keaton hosted a memorial program on PBS dedicated to his friend and mentor.
Placards seen at "Gangster Arms" said "Legs & Shirley Diamond"; "Pretty Boy & Pretty Girl Floyd"; "Al & Cindy Capone"; and "Johnny Dangerously". (Al Capone's wife was actually named Mae, and looked nothing like the Mrs. Capone in the movie.)
Rival gangster Maroni's butchering of the English language is a parody of the stereotypes of Italian immigrants in old movies who have exaggerated accents and speak poor English. The parody is carried further still whenever Maroni swears.
The 'Film Yearbook Volume 4' said that this movie was a "parody burlesque of Warner Brothers gangster films". The picture ironically though wasn't made at Warners, the film was made at 20th Century Fox.